Pulsed high pressure discharge pumped gas lasers, for example excimer lasers or transversely-excited atmospheric (TEA) CO2 lasers, require a gas recirculation loop to cool and renew the gas in the discharge area between each pulse to obtain a stable and homogeneous irradiation beam.
An example is found in FR2718894 A1, wherein a gas circulation loop is described mounted in line with the discharge area (see FIG. 1). A drawback of this design is that, since the gas is renewed in axial direction to the discharge tube, the homogeneity of the gas along the full length of the discharge area cannot be guaranteed.
Moreover, gas renewal in axial direction over the full length of the discharge tube occurs insufficiently fast when operating at high pulse rates.
Another example of a gas circulation loop, which alleviates the above problem is shown in FIG. 2. This well-known type of gas circulation loop is a wind tunnel type circulation loop renewing the gas in transversal direction to the discharge area.
A disadvantage of a wind tunnel type circulation loop is that, using traditional design rules of aerodynamic wind tunnels to create the required gas flow speed and gas flow homogeneity, it can have a rather large size. Particularly, when using it for discharge tube volumes up to 2 m×0.1×0.1 m, the design rules can lead to such extremely large sizes that incompatibility with industrial environment may become a problem.
Another already more compact type of a gas circulation loop renewing the gas in transversal direction and designed for improving homogeneity of the gas along the full length of the discharge area is disclosed in DE 199 36 955. It comprising a gas supply duct and a gas exhaust duct elongated in the longitudinal direction of the laser discharge tube and comprises a number of respective inlet channels and outlet channels. However, homogeneous renewal of the gas in this design is still not satisfying, in particular not for high pulse rates.
Considering the above drawbacks, it is an object of the present invention to provide a gas circulation loop even more improving homogeneity of the gas along the full length of the discharge area.
Another object is to provide a gas circulation loop enabling sufficiently fast gas renewal for operating at high pulse rates.
Further, it is an object of the present invention to provide a compact gas circulation loop that is acceptable in size for use in industrial environment, even in combination with very large discharge tubes.